ignition timing while driving question

[RumpRanger98]

I was checking out my scanner that has live data today while driving around. I noticed the ignition timing would fluctuate alot depending on throttle.

Cruising, steady foot on pedal, 2800 rpms it would be at 38*
foot off pedal from cruising/accelerating 13*
accelertaing was multiple, more 20* and 25*

so when I would cruise engine at 2800rpms the timing would be 38* or very close and as soon as I would give more gas the timing would drop to the 20's,


Im just curious if this is normal?

I always thought timing was suppose to be set at one spot and didnt fluctuate unless told to by detonation sensor.

 

[martin]

judging by your figures your system seems to be performing perfectly.

 

[srteach]

It's important to give the truck information. When writing a reply, you don't get to see the signature.
I don't see what truck you are talking about, but I assume the '98 in your name is what truck it is. No idea what engine. No idea what drivetrain.
That being said, the timing will vary based on engine load, fuel input, throttle input, exhaust gasses, engine temp, engine speed, and other sensor readings.
Most of this is for emissions, but it does help efficiency.

38 btdc may be a bit much for cruise (I would expect about 30 btdc), but cruising at high RPM will cause timing to advance in order to burn all the fuel put into the engine. The timing retardation when going from cruise to acceleration is about normal, usually to about 20-25 btdc. This assures the fuel is burned on the expansion stroke of the cycle for more power, even though it is less efficient. Idle uses very little fuel, so has a very small advance (called base timing) of about 8-10 btdc. An immediate 13 btdc at pedal release is to be expected. When you take your foot off the pedal to idle, it will take 2-3 minutes to get to base timing.

Depending on the engine, you may or may not have a detonation sensor.

 

[RumpRanger98]

sorry was just looking for a general answer if that sounded normal for timing. I kinda thought 38* was a bit high

but its a 99 ranger 4x4 3.0 v6 5speed